1. Field of the Invention
The present invention relates to an image forming device, such as a laser printer.
2. Description of the Related Art
Image forming devices such as electrophotographic laser printers are well known in the art. A developer cartridge accommodating toner can be detachably mounted in this type of image forming device.
The developer cartridge includes a toner compartment and a developing section. The toner compartment is filled with toner and includes an agitator that can be driven to rotate. The developing section includes a supplying roller, a developing roller, and a thickness regulating blade. The supplying roller and the developing roller are juxtaposed and in contact with each other. The thickness regulating blade applies pressure to the surface of the developing roller.
When the developer cartridge is mounted in the laser printer, motive power from the laser printer is transferred to the developer cartridge through a gear train. As a result, the agitator rotates and conveys toner from the toner compartment to the developing section. Also, the supplying roller to supply the toner onto the developing roller. The toner is tribocharged between the supplying roller and the developing roller at this time. Further, as the developing roller rotates, toner on the surface of the developing roller passes between the thickness regulating blade and the developing roller and is regulated to a layer of uniform thickness on the surface of the developing roller.
The developer cartridge is disposed in the laser printer with the developing roller in opposition with a photosensitive drum of the laser printer. The photosensitive drum is formed on its surface with an electrostatic latent image. When rotation of the developing roller brings the toner on the surface of the developing roller into contact with the photosensitive drum, the toner moves onto and develops the electrostatic latent image into a toner image. The toner image is then transferred onto the surface of a sheet by operation of a transfer roller.
Conventionally this type of image forming device includes a toner sensor for detecting the amount of toner remaining in the toner compartment.
Normally the toner sensor is an optical sensor that includes a light-emitting element and a light-receiving element. Also, light-transmissive windows are provided in opposite walls of the toner compartment. The light-emitting element and light-receiving element are positioned one on the outside of each transmissive wall so as to face each other through the light-transmissive windows.
The toner sensor outputs a light detection signal to a CPU in the laser printer each time the light-receiving element receives light emitted from the light-emitting element. The CPU determines the amount of toner remaining in the toner compartment based on the percentage of light received by the light-receiving element. The CPU then selectively displays data indicating the remaining toner status, such as “full state,” “low state,” “empty state,” on a display panel of the laser printer.